Organic waste treatment apparatus

ABSTRACT

A composting system including a vertically-orientated vessel with mechanisms attached to a vertically oriented central mounted rotating shaft, including rotatable size reduction blade(s), agitation mechanism(s), and discharge blade/mechanism(s). The composting system includes internal size reduction mechanism for reducing the size of material introduced to the vessel. The composting system includes a loading hatch, a discharge hatch, and a source of air to maintain aerobic conditions within the vessel. In use, material introduced moves from the upper region of the vessel gravitationally and via agitation through a zone of size reduction to the lower region of the vessel. Process conditions within the vessel are controlled by an operator and via electronic control mechanism, which can monitor operating conditions such as temperature and loading rate (for example), to manage air injection, mechanical agitation and size reduction such that composting proceeds efficiently and at an optimal rate.

FIELD OF THE INVENTION

The present invention relates to the field of waste treatment,particularly food waste treatment. The present invention provides anovel waste treatment apparatus which may be used, for example, as anon-site waste treatment vessel at businesses where significant amountsof food waste are produced (e.g., accommodation enterprises, fruit andvegetable shops and markets, retirement villages and multi-unitdwellings, supermarkets, restaurants/cafes/cafeterias, governmentworkplaces, and hospitals).

BACKGROUND TO THE INVENTION

Any discussion of the prior art throughout the specification should inno way be considered as an admission that such prior art is widely knownor forms part of common general knowledge in the field.

Food waste and other putrescible organic waste is a major contributor tothe cost of waste disposal. This is due largely to the present need totransport such wastes to specific landfill sites which are often atsignificant distances from the sites of the waste production. Inaddition, the disposal of wastes such as food waste and otherputrescible organic waste is particularly undesirable due to their highwater and nutrient content, leading to the release of organic acids andother compounds during anaerobic decomposition which are majorcontributors to the negative environmental impacts associated withlandfills (Recycled Organics Unit, 2001a, Greenhouse gas emissions fromcomposting facilities, Report for Central Coast Waste Board, NSW,September 2001). Indeed, food waste is the second largest source ofmethane in landfills (behind paper and cardboard) (US EPA, 1998,Greenhouse gas emissions from management of selected materials inmunicipal solid waste, United States Environmental Protection Agency.).The nutrients present in food waste also contribute to the high nutrientand heavy metal loadings in landfill leachate, and is a majorcontributor to groundwater and surface water contamination in regionswith unlined landfills (Russel and Higer, 1988, Assessment ofgroundwater contamination near Lantana landfill, southeast Florida,Ground Water, 26(2): 156-164; Borden and Yunoschak, 1990, Ground andsurface water quality impacts of North Carolina sanitary landfills.Water Resources Bulletin, 26(2): 269-277; Assmuth and Strandberg, 1993,Groundwater contamination at Finnish landfills, Water, Air and SoilPollution, 69 (1/2):179-199).

In addition to the environmental concerns regarding the landfilldisposal of putrescible food and organic wastes, in many countriesincluding Australia, the available landfills are reaching capacity. Forexample, in Sydney, present landfill capacity for putrescible food andorganic wastes in the Greater Sydney Region is expected to be exhaustedby 2011, based upon current levels of waste generation and recyclingrates (Wright, 2000, Independent Public Assessment—Landfill Capacity andDemand, Report prepared for the Minister of Urban Affairs and Planning,State Government of NSW, September 2000). Such shortages of landfillsites, and the resistance of communities to the establishment of newlandfill sites on health, environmental and monetary concerns, isurgently impelling the need to divert recyclable wastes from landfill.Indeed, many Governments have now developed policies to reduce landfilldisposal of putrescible food and organic wastes (e.g., the NSWGovernment policies, ‘Waste Not’ Development Control Plan (DCP) andWaste Reduction and Procurement Policy). However, the meaningfulimplementation of these policies mandates the identification anddevelopment of practical alternatives to landfill disposal.

The present invention is directed at the provision of a simple and costeffective waste treatment apparatus, which may be readily used by wasteproducers, to decompose food and other putrescible organic wastes to auseful composted waste material product and thereby divert such wastesfrom landfill disposal. The composted waste material product can be usedto improve soils, plants and the environment in which we live.

There are four main types of composting systems that have been devisedfor commercial purposes, however, hybrid systems are also available. Thefour main systems can be categorized as follows:

A windrow system: this is an open system and the material to becomposted is piled in long rows. These are aerated by forced convectionor by frequent turning using a mechanical agitator system.

An enclosed static stack system: air is forced up through the pile ofthe material to be composted, which is enclosed is some type of vessel.This is a batch process in which the vessel is loaded and unloaded oncefor each composting cycle.

An agitated bay system: these systems primarily utilize U-shapedchannels or bays. Material to be composted is often addedsemi-continuously and periodically agitated and moved by mechanicalmeans. However, primary aeration is often achieved via forced airmovement.

Continuous or semi-continuous in-vessel composting systems: in thesesystems the material to be composted is fed in one end (side, top orbottom) of the composting systems and exits continuously from the other.

Numerous examples of the above systems are currently being produced andare illustrated in “The Practical Handbook of Compost Engineering”,Roger T Haug, Lewis Publishers, 1993 (ISBN 0-87371-373-7).

It is an object of the present invention to overcome or ameliorate atleast one of the disadvantages of the prior art, or to provide a usefulalternative.

An object of the present invention, at least in a preferred embodiment,is to provide an in-vessel, semi-continuous and generally verticalcomposting system, which provides an efficient alternative to existingcomposting systems.

SUMMARY OF THE INVENTION

Thus, in a first aspect, the present invention provides an apparatus foraerobically composting waste material, the apparatus comprising:

an enclosed vessel comprising a top wall, base wall and side wall(s)defining an interior vessel space;

a rotatable shaft located within said vessel space;

a drive means operatively connected to said rotatable shaft for drivingsaid shaft;

size reduction means mounted on said rotatable shaft for reducing thesize of waste material introduced to the vessel, wherein said sizereduction means divides the interior vessel space into first and secondregions and defines a zone of size reduction through which all wastematerial must pass as it passes through the vessel;

a loading port through which waste material may be introduced to saidfirst region of the vessel;

a discharge port through which waste material may be removed from thesecond region of the vessel; and

a source of oxygen to maintain aerobic conditions within said vessel,wherein, when the apparatus is in use, waste material introduced to saidvessel moves from said region through the size reduction means to saidsecond region.

The vertically-orientated vessel may be constructed of any suitablematerial, but is preferably constructed of stainless steel or likecorrosion-resistant material. The walls, and particularly the sidewall(s), are preferably insulated so as to retain heat generated byaerobic composting of introduced waste material. The volume of theinternal vessel space is preferably within the range of 1.5 to 5.0 m³,more preferably, 2.0 to 3.0 m³. In a particularly preferred embodiment,the volume of the internal vessel space is about 2.5 m³. This volume issufficient to enable an apparatus according to the present invention tocompost about 1230 kg of food waste material per week.

The size reduction means is provided so as to reduce the size ofintroduced waste material to particles/pieces of an averagediameter/dimension size of approximately 2 to 10 mm. It has been foundthat by reducing the size of introduced waste material toparticles/pieces greatly increases the rate of composting which may beachieved and assists in the production of a well mixed and uniform,composted product. The size reduction means also assists in the thoroughmixing of the introduced waste material. The apparatus is preferablyarranged so that all waste material must pass through the size reductionmeans when passing from the upper region to the lower region of thevessel.

The size reduction means preferably comprises a plurality of bars,blades or cutting plates. The bars, blades or cutting plates do not needto be sharp as the size reduction may be achieved through mechanicalshearing and tearing. The bars, blades or cutting plates may thereforetake the simple form of flat bars, preferably with beveled edges and/orsharp edges. Preferably, at least one of the bars, blades or cuttingplates is adapted for movement (e.g., by horizontal rotation). Morepreferably, the size reduction means comprises two or more, horizontallyrotatable bars, blades or cutting plates, and two or more fixed (e.g.,mounted to the side wall(s)), horizontally disposed and parallel bars,blades or cutting plates, wherein at least one of the horizontallyrotatable bars, blades or cutting plates rotates within a parallel spacebetween two of said fixed bars, blades or cutting plates. Preferably,the parallel space between said two of said fixed bars, blades orcutting plates is in the range of 10 to 200 mm in width, more preferably100 to 150 mm in width. The width of the rotatable and fixed blades orcutting plates may be substantially alike and, preferably, is within therange of 50 to 100 mm. The bars, blades or cutting plates may beconstructed of any suitable material, but are preferably constructed ofstainless steel or like corrosion-resistant material.

The loading hatch may be located in the side wall(s) adjacent to the topwall, but more preferably, is located in the top wall. The loading hatchmay be conveniently adapted for controlled or automated opening andclosing. Preferably, the loading hatch, when closed, forms an air-tightseal to prevent escape of any odorous gas or “process air” from thevessel.

The discharge hatch may be located in the side wall(s) adjacent to thebase wall, but more preferably, is located in the base wall. Thedischarge hatch may be conveniently adapted for controlled or automatedopening and closing. Preferably, the dispatch hatch, when closed, formsan air-tight and liquid seal to prevent escape of any odorous gas orprocess air and liquids (i.e., leachates) from the vessel.

The apparatus is provided with a source of oxygen (e.g., a source ofcompressed air), to maintain aerobic conditions within the vessel. Thisis important in order to achieve composting by aerobic microorganismsrather than anaerobic microorganisms which tend to produce greaterquantities of odorous gas. The supply of oxygen may be controlled orautomated so as to provide sufficient oxygen to maintain the optimumtemperature and oxygen conditions in the vessel for composting byaerobic mesophilic and thermophilic microorganisms (e.g., temperature ofabout 50-55° C.). Automated control of oxygen supply may be achieved byproviding a temperature sensor within the vessel. When the temperaturedrops to below a first set temperature (e.g., 45° C.), as measured bythe temperature sensor, the supply of oxygen is activated in a mannerthat causes an increase in temperature to approximately 50° C. Also,when the temperature increases to above a second set temperature (e.g.,60° C.), as measured by the temperature sensor, the supply of oxygen isactivated to blow off excess heat until a temperature of approximately55° C. is achieved. The temperature sensor is preferably located in thelower region of the vessel in a position within 250-450 mm of the basewall. Supplied oxygen enters the vessel by one or more inlets, which arepreferably located in the side wall(s) adjacent to the join with thebase wall and also in a central location in the base wall. The apparatusis provided with at least one outlet, preferably located in or adjacentto the top wall, to discharge odorous gas or process air from within thevessel. This process air may be discharged to the atmosphere via vent orvia an odor scrubber to remove any odorous gases.

Movement of the bars, blades or plates is conveniently achieved bymounting the bars, blades or cutting plates on a rotatable shaft, havinga vertical axis of rotation, which is preferably mounted on the basewall and, preferably, the top wall, such that the rotatable shaftrotates centrally within the vessel. The rotatable shaft may beconstructed of any suitable material, but is preferably constructed ofstainless steel or like corrosion-resistant material. The rotatableshaft may be driven by any suitable means (e.g., an electric motor), andmay be adapted for continuous operation or, more preferably, controlledand/or automated, intermittent operation. The rotation of the rotatableshaft may be at a speed within the range of 5 to 60 rpm, but morepreferably, within the range of 10 to 30 rpm.

Such a rotatable shaft may also be provided with fittings, other thanthe one or more blades or cutting plates. For example, on a portion ofthe rotatable shaft that resides within the upper region of the vessel,there may be provided one or more spreader or mixer bar(s) to assist inevenly distributing and mixing introduced waste material. Also, on aportion of the rotatable shaft that resides within the lower region ofthe vessel, there may be provided one or more mixing bar(s) to ensurethat the waste material in the lower region of the vessel is moved byagitation therefore ensuring even and consistent flow of compostingmaterials. Further, on a portion of the rotatable shaft adjacent to thebase wall, there may be provided one or more sweeper bar(s) or plate(s)to sweep composted material adjacent to the base wall towards and out ofthe discharge hatch. The rotatable shaft preferably operates both in aclockwise and anti-clockwise direction, and all rotating bars and bladesor cutting plates are preferably symmetric is plan view to allow foreffective action in both directions.

In a second aspect, the present invention provides a method of producinga composted product using an apparatus for aerobically composting wastematerial, said apparatus comprising:

a vessel comprising a top wall, base wall and side wall(s) defining aninterior vessel space;

a rotatable shaft located within said vessel space;

a drive means operatively connected to said rotatable shaft for drivingsaid shaft;

size reduction means mounted on said rotatable shaft for reducing thesize of waste material introduced to the vessel, wherein said sizereduction means divides the interior vessel space into first and secondregions and defines a zone of size reduction through which all wastematerial must pass as it passes through from input end to discharge endof the vessel;

a loading port through which waste material may be introduced to saidfirst region of the vessel;

a discharge port through which waste material may be removed from saidsecond region of the vessel; and

a source of oxygen to maintain aerobic conditions within said vessel,

wherein said method comprises introducing said waste material into saidfirst region of the vessel through said loading port, passing said wastematerial through said size reduction means to reduce the size of thewaste material, whilst maintaining conditions within said vesselsuitable for aerobically composting said waste material.

Preferably, the waste material is introduced to the vessel with asuitable absorbent or adsorbent material (e.g., wood shavings orsawdust) to reduce any excess amounts of moisture or liquids in thewaste material. The waste material may be, if desired, pre-mixed withthe adsorbent or absorbent material prior to introduction into thevessel. Preferably, the adsorbent or absorbent material and wastematerial is introduced into the vessel in a ratio (on a weight to weightbasis) of 1:8 to 1:2, more preferably, 1:4 to 1:5.

In a third aspect, the present invention provides a composted productproduced in accordance with the method of the second aspect.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise”, “comprising”, and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.”

BRIEF DESCRIPTION OF ACCOMPANYING FIGURES

One or more embodiments of the invention will now be described, by wayof example only, with reference to the accompanying drawings in which:

FIG. 1 shows a longitudinal section view of an organic waste treatmentapparatus according to the present invention.

FIG. 2 provides a plan view of a particular embodiment of a sizereduction means which may be employed in an organic waste treatmentapparatus shown in FIG. 1. The embodiment comprises spiked, fixed androtating size reduction blades.

FIG. 3 provides graphical results of temperature and interstitial oxygenconcentration changes during a seven week composting trial of theapparatus described in Example 1. In this trial, a temperature feedbackmechanism provided in the apparatus was programmed to a set-point of 50°C.

FIGS. 4 a, 4 b and 4 c provide graphical results of temperature andinterstitial oxygen distribution at different depths in the compostingchamber during a seven week composting trial of the apparatus describedin Example 1. The results shown are typical of that generated over theduration of the trial. FIG. 4 a: 300 mm from the top of the compostingmass, FIG. 4 b: middle of the chamber (900 mm above base), and FIG. 4 c:bottom of chamber (300 mm above base).

DETAILED DISCLOSURE OF THE INVENTION

FIG. 1 shows a waste treatment apparatus or compostor according to thepresent invention. The apparatus comprises a generally cylindricalvessel or chamber (1) with insulated side walls (2) and top wall orceiling (3) comprising a suitable insulation material (4) (expandedfiberglass baits) sandwiched between an inner vessel (5) generallyconstructed of stainless steel or like corrosion-resistant material andan outer shell (6). The chamber further comprises a base (7), alsoconstructed of stainless steel or like corrosion-resistant material,including a discharge outlet or hatch (8). When closed, the dischargehatch forms an air and liquid tight seal. The ceiling (3) of the chamber(1) is provided with a loading hatch (9) which closes in an air-tightmanner. The loading hatch may be operated manually, or automatically bya pneumatic cylinder (10) controlled via a simple switch (11). With thedischarge and loading hatches (8, 9) closed, the chamber (1) issubstantially sealed from the atmosphere.

The chamber (1) is provided with a source of compressed air (12) (e.g.,an air compressor or cylinder of compressed air) which provides air,under positive pressure, through a number of inlets (13) located in thelower regions of the side walls and via the lower bearing housing in thebase (7). In the ceiling (3), an outlet (14) is provided for escape orremoval of process air and gases. The outlet (14) may be connecteddirectly to atmosphere via a vent stack, or may be piped incommunication (15) with a scrubber (16) for removal of odors from theprocess air and gases, and an air/gas discharge outlet (17) to theatmosphere. The scrubber may be in communication with a condensatedischarge outlet (38).

The exterior of the chamber (1) may be equipped with an automated binloading mechanism (18) (e.g., a garbage bin lifting mechanism) tointroduce waste materials directly from a bin (19) into the chamber (1)through the loading hatch (9). The exterior of the chamber (1) may alsobe equipped with a ladder (20) to provide ready access by an operator.

In the interior of the chamber (1), at a position adjacent to theloading hatch, is provided one or more a spreader or mixer bar(s) (21)to assist in evenly distributing and mixing introduced waste materialsacross the area of the upper section of the chamber (1). The spreaderbar(s) (21) are perpendicularly mounted upon a rotatable, centrallylocated, vertical shaft (22), so that the spreader bar(s) are slowlyrotated (e.g., 10 to 30 rpm). Below the spreader bar(s) (21), areprovided fixed and/or moving blades or cutting edges (23-28) whichreduce the size of the waste material and achieve further mixing. In theembodiment shown in FIG. 1, these blades or cutting edges comprise: apair of blades (23) perpendicularly mounted upon the rotatable shaft(22) and which extend such that the distal ends of the blades areclosely adjacent to the side walls (2) of the chamber (1); a pluralityof blade pairs (25, 27) mounted to the rotatable shaft of a lesserextension to the pair of blades (23); and a plurality of fixed blades(24, 26, and 28) mounted to the side walls (2) of the chamber (1). Allspreader bar(s) and blades are constructed of stainless steel or likecorrosion-resistant material. The fixed and rotatable blades (23-28)cooperate to ensure that the waste material is reduced to particles orpieces of small dimension (typically 2 to 10 mm in length or diameter),and thoroughly mixed, thereby maximizing exposure of the putrescible andcompostablc waste material to the mechanical and biological processeswithin the chamber. The fixed and rotatable blades (23-28) also ensurethat any biodegradable plastic packaging material present in the wastematerial is torn or shredded into particles or pieces of smalldimension. To assist with the tearing or shredding of biodegradableplastic packaging, at least one of the blades or cutting edges may beprovided with short spikes or teeth (FIG. 2).

Further rotatable mixing bar(s) (29) may be provided to ensure that thewaste material that has passed through the fixed and rotatable blades orcutting edges (23-28) are moved by agitation.

The rotatable shaft (22) is driven by any conventional means such as adrive motor (30) equipped with a gearbox to allow clockwise andanti-clockwise rotation. Bearing housings (31, 32) are shown below theceiling (3) of the chamber (1) and below the base (7).

At the base (7) of the chamber (1), there is provided a dischargemechanism comprising a sweeping bar or plate (33) mounted to therotatable shaft (22) which sweeps composted product towards and out ofthe discharge hatch (8) for discharge to a collection bin or trolley(34) which may be positioned under the chamber (1) and between thechamber support legs (35).

The chamber is further provided with a wall mounted thermistor probe (orequivalent) (36), which is connected to an electronic control mechanismin a control box (37). This provides a temperature feedback mechanismwhich monitors the temperature of the composting waste material andsupports automated control of compressed air supply to the chamber (1)via the air compressor (12) and associated air inlets (13). The controlbox (37) is preferably lockable and contains electronic componentry tocontrol the composting process, and a safe and user friendly interfacefor the operator (control panel). The drive motor (30) for the sweepingbars (33), blades (23-28), spreader bar(s) (21) and mixing bar(s) (29)can be controlled by the operator at the control box (37), and/orautomatically via a timer mechanism. In addition, the air compressor(12), which forces air under positive pressure into the composting wastevia the air inlets (13), can also be controlled manually by the operatorvia the control box (37), and/or automatically via the temperaturefeedback mechanism described above.

The chamber operates under continuous (or plug) flow principles. In use,food waste or other putrescible organic waste is introduced into thechamber (1) through the loading hatch (9) onto an existing compostingmass of previously introduced waste. The wastes may be introduced withan absorbent or absorbent material such as wood shavings or sawdust. Thechamber (1) is preferably filled to a level just above the spreaderbar(s) (21). The loading hatch (9) (and discharge hatch (8)) is thenclosed and the composting process commenced by activating the electroniccontrol mechanism at the control box (37). Composted product may beremoved from the chamber through the discharge hatch (8) to createadditional space in the lower region of the chamber (1). Theremoval/discharge of composted product allows the composting mass tomove lower into the chamber (1) under the force of gravity andmechanical agitation, creating space in the upper region of thecomposting chamber for the addition of more waste material. One or moredistribution or spreader bar(s) (21), blades (23, 25, and 27), andmixing bar(s) which are mounted to the rotatable shaft (22) rotate inunison once the chamber is sealed and the composting process activatedat the control box (37). The rotation, and direction of rotation, of therotatable shaft (22) is operated automatically via an electronic timingmechanism so as to operate throughout the day for short periods of time.The rotation, and direction of rotation, of the rotatable shaft can bemanually or automatically operated via the control box (37). Inoperation, the spreader bar(s) (21) mixes and spreads the recentlyloaded waste material evenly above the cutting blades (23-28). Theblades (23-28) cooperate to form a “size reduction zone” through whichall waste material must pass and which reduces the particle/piece sizeof the waste material, and destroys any containers or packaging presentso as to expose the waste material to the mechanical and biologicalprocesses within the chamber (1). That is, the size reduction increasesthe surface area for microbial decomposition of the waste material, andresults in more rapid composting. Further mixing and agitation of wastematerial occurs at various levels throughout the composting chamber (1).

Temperature is sensed by a thermistor probe (36) and monitored by theautomated electronic control mechanism in the control box (37). The aircompressor (12) is activated automatically in response to temperature inorder to maintain a consistent temperature within the composting wastematerial mass of about 55° C. which is characteristic of the optimumrate of aerobic microbial decomposition. The air compressor (12) canalso be operated manually by the operator (i.e., to allow forintervention, for example, where excessively wet waste material has beenloaded such that there is a need for additional aeration to drive offexcess moisture) via the control box (37). The controls are, however,usually and conveniently set to “auto” so that aeration can be managedautomatically by the temperature feedback mechanism described above.When the thermistor probe (36) senses a change in chamber temperature toless than 50° C., the temperature feedback mechanism results in theaddition into the chamber (1) of compressed air from the air compressor(12) via air inlets (13) located in the base (7) adjacent to the sidewalls (2) and in the lower bearing housing (32) so as to maintainoptimal aerobic conditions throughout the composting mass. Since thechamber is also insulated to retain heat, the chamber is able to beoperated to maintain substantially optimal aerobic and thermophilicconditions, thereby ensuring pasteurization and maximizing the rate ofcomposting of the waste material.

The placement of one or more air inlets (13) in the lower bearinghousing (32) also assists in keeping the housing (32) free of wastematerial.

Air which has passed through the waste material contained within thechamber (1) is forced from the top or headspace of the chamber (1) underpositive pressure through the outlet (14) and ducting (15) to directdischarge to atmosphere via a vent stack, or to an odor scrubber (16)for treatment prior to discharge. A corrosion resistant fan is typicallyprovided to assist in drawing air out of the headspace of the chamber(1) to the scrubber (16). Moisture in the process air condenses intoliquid upon cooling in the ducting and is removed via the condensatedischarge outlet (38), which can be plumbed directly into a sewer ifrequired (usually only if an odor treatment unit is installed).

Composted product can be removed from the base (7) of the chamber (1)through the discharge hatch (8) to fall freely into a dischargecollection bin or trolley (34). The sweeping bar(s) (33) activelydischarges composted product from the discharge hatch (8).

The present invention allows the provision of a self-contained andautomated waste material handling and processing system which may beused on-site (e.g., accommodation enterprises, fruit and vegetable shopsand markets, retirement villages and multi-unit dwellings, supermarkets,restaurants/cafes/cafeterias, government workplaces, and hospitals). Thesystem allows for the efficient conversion of putrescible food andorganic wastes (e.g., food, meat and other high strength wastes, sawdustand wood shavings, and pre-shredded paper and cardboard packagingwastes) into a composted waste material product for garden oragricultural use.

The invention will hereinafter be further described by way of thefollowing non-limiting example(s).

Example 1 Materials and Methods

Description of the Apparatus and Process.

A trial was conducted to objectively characterize the performance of anorganic waste treatment apparatus according to FIG. 1, in terms ofprocessing performance (i.e., retention time and processing capacity),product quality and stability, and associated environmental impacts(e.g., odor, pests and leachate).

The apparatus was designed for on-site conversion of food waste into asaleable composted waste material product, which would be capable ofbeing operated by a single user.

The apparatus comprised a composting chamber with an internal volume of2.4 m3. The apparatus was provided with an analogue temperature feedbackmechanism (comprising a digital thermostat controller) controlled theinjection of compressed air from two reciprocating air compressors via aring main installed on the bottom outer perimeter of the compostingchamber and into a bearing housing at the base of a central rotatableshaft. Injection of air occurred continuously until the composting massreached a temperature of 50° C., at which point it was turned off, toallow composting to proceed optimally. Fixed cutting blades were fittedwith short spikes to assist in the shredding and tearing ofbiodegradable plastic bags, so as to ensure that if any bags of thiskind were introduced into the chamber, then they would be shredded ortorn and thereafter evenly mixed into the composting mass. Three sickleshaped mixing bars mounted on the central rotatable shaft of theapparatus were provided to assist in mixing of the composting mass. Thesize reduction means and mixing system was operated at 30 rpm and wasdriven by a 11 kW electric motor housed beneath the chamber. Mixing ofthe composting mass was automatically controlled to provide mixing forapproximately 60 seconds once a day.

Source separated food waste was collected in 80, 120 or 240 L wheeliebins and loaded into the composting chamber of the apparatus via aloading hatch with an integrated 150 kg lift capacityelectrically-driven bin-lift unit.

Feedstock Collection and Preparation.

Combined pre- and post-consumer food waste was sourced from a commercialcatering enterprise in 120 L wheelie bins that were lined with Biocorp™biodegradable bags (corn starch polymer based). Approximately 1 ton offood waste was collected per week, and was temporarily stored in a coolroom at 2° C. prior to transport and loading into the apparatus.

Wood shavings in 240 L chaff bags was used as a bulking agent to assistin the composting of the food waste to increase the carbon: nitrogen(C:N) ratio and to reduce the moisture content. The moisture content andC:N ratio of a representative 1 L sample of food waste and wood shavingswas determined according to Australian Standard AS 4454 (1999). Thisdata was used to prepare a waste mix to achieve a C:N ratio of 20:1 anda moisture content of approximately 65-68%, which is the upper maximumfor rapid composting.

Operation of the Apparatus.

Approximately 210 kg wood shavings and 1000 kg food waste was loadedinto the apparatus so that approximately 80% of the chamber was filledwith the waste mix. All materials were weighed on a Wedderburn 100 kgplatform scale prior to loading. To ensure that an appropriatecomposting waste material mix was obtained, one (weighed) 240 L bag ofwood shavings was loaded into a 240 L wheelie bin and deposited into theapparatus via the bin lift. This was followed by approximately 100 kgfood waste (approximately 1.5 120 L wheelie bins), with continuousmixing. The food waste was layered in the unit until all materials wereloaded, under constant agitation via the internal mixing system toensure that the food waste was fully incorporated into the woodshavings, and to ensure that the food waste was size reduced(particularly for hard food waste components, such as pumpkins).

The apparatus was left for one week to build up temperature beforeregular reloading occurred.

Based on the volume on the composting chamber, initial density of thefood waste/wood shaving mix, and the volume reduction following mixingand size reduction, it was calculated that the apparatus compostingvessel could process up to approximately 1230 kg of food waste per week.

A loading schedule was then developed so that a range of samples couldbe extracted from the vessel with different retention times. The plannedloading schedule is shown in Table 1 below:

TABLE 1 Planned food waste loading schedule to determine processingperformance of the apparatus and resulting product quality at a range ofretention times from approximately 1 to 4 weeks. Week Food waste Woodshaving Total material Estimated retention Estimated retention endingloaded (kg) loaded (kg) loaded (kg) time (days) time (weeks) 1 1000215.2 1215.2 8.6 1.2 2 700 150.6 850.6 12.3 1.8 3 500 107.6 607.6 17.22.4 4 300 64.6 364.6 28.1 4.0 5 300 64.6 364.6 28.1 4.0 6 300 64.6 364.628.1 4.0 7 300 64.6 364.6 28.1 4.0

To reduce labor requirements, food waste and wood shavings were loadedonce per week with the desired weekly quantity. After the loading ofeach batch, the apparatus was sealed and left to process the food wasteand wood shavings mixture. After each loading, plastic markers wereadded to the top of the composting waste material mass in the upperregion of the chamber so that individual loadings could readily beidentified on discharge of the composted waste material product.

An extended processing duration for the lower loading rates wasperformed (i.e., 300 kg/week for weeks four to seven) as it wasestimated that at least 4 weeks would be required from the loading untilthe waste material traveled through the chamber to be available fordischarge.

Samples of composted waste material product representing a retentiontime of approximately one, two, three and four weeks duration wereextracted from the unit on weeks two, three, four and seven.

Approximately 5 L of composted waste material product wasrepresentatively sampled, bagged and stored at 0° C. prior to analysisfor pH, electrical conductivity and moisture content according toAustralian Standard AS 4454 (1999). A sample after one week retentiontime was analyzed for compliance as a pasteurized mulch according toAustralian Standard AS 4454 (1999).

Apparatus Performance Analysis.

Temperature and interstitial oxygen profiles were recorded with agalvanic cell type combined oxygen/temperature probe (Demista®, USA)over the seven week trial to determine the efficiency of the aerationand temperature control system. Temperatures and interstitial oxygenprofiles were taken at 300, 600 and 900 mm from the central rotatableshaft at various depths in the chamber to characterize the temperatureand oxygen profiles in vertical and horizontal sections of the chamber.

The percentage of time that the air compressors were operating tomaintain the thermostat set point temperature of 50° C. was determinedby fitting a Dickson 5120 temperature data logger into the process airoutlet. Changes in the temperature of the process air indicated when theair compressors were operational and blowing off heat from thecomposting waste material mass.

A number of qualitative observations were also made to characterize theperformance of the apparatus during the trial, including whether air orleachate leaked through the discharge hatch; the presence or absence ofleachate at the base of the apparatus; ease of loading materials intothe loading hatch with the bin lift; case of discharge of compost intothe discharge trolley; electrical current draw by the drive motor;efficiency of the size reduction and mixing system, and odor levelemitted by the gas cleaning unit prior to discharge to the atmosphere.

Results and Discussions

Chemical and Physical Characteristics of Feedstock Materials.

The chemical and physical characteristics of food waste (including meat,dairy and seafood fractions), wood shavings and the combined foodwaste/wood shavings feedstock mix is shown in Table 2. As expected, themoisture content of food waste alone was very high −79.8%. This highmoisture content was in part due to the fact that the food waste streamcomprised post-consumer food waste, including pasta and cream/meatsauces. Due to the high moisture content and poor structure, addition ofa carbonaceous bulking agent was highly preferred so as to absorb excessmoisture, increase the C:N ratio, and to increase the air-filledporosity of the mix to ensure that adequate air flow and adequatecomposting can take place (Jackson and Line, 1998, Assessment ofperiodic turning as an aeration mechanism for pulp and paper mill sludgecomposting, Waste Management and Research, 16(4): 312-319).

TABLE 2 Chemical and physical characteristics of individual and combinedfeedstocks processed in the trial over an 8 week period. MoistureElectrical Organic Total Bulk Feedstock content Conductivity CarbonNitrogen C:N density Component (%, w/w) pH (dS m⁻¹) (%, w/w) (%, w/w)ratio (kg m³) Food waste 79.8 5.0 4.45 54.6 5.20 10.6 658.5 Wood 14.86.3 0.02 57.5 0.09 641.0 75.9 shavings Food waste and 68.9 5.5 0.92 56.12.80 20.0:1 430.2 shavings

Addition of wood shavings also slightly increased the pH of the foodwaste, and significantly reduced the electrical conductivity of the foodwaste component. The pH and electrical conductivity of the foodwaste/wood shavings mix were ideal for rapid composting (Miller, 1993,Composting as a process based on the control of ecologically selectivefactors, In: F. Blaine Metting Jr. (ed.), Soil Microbial Ecology:Applications in Agricultural and Environmental Management, Marcel DekkerPublishing, New York, pp 515-544). Wood shavings were also found to bevery effective is absorbing excess moisture released by the food wastefraction, making it more amenable to composting, and also advantageouslyavoiding the potential for leachate formation. Leachate can be a majorproblem for waste management, as the leachate can be odorous, unsightly,can attract pests/vermin and has a high biological oxygen demand, makingit difficult to handle.

TABLE 3 Feedstock recipes for processing food waste at different C:Nratios in the apparatus. Addition of greater quantities of food waste toachieve a C:N ratio less than 20:1 is not advisable due to the potentialfor leachate formation in the bottom of the composting chamber. Thiswould increase the moisture content of the processed compost, making itdifficult to store and handle. Moisture Content Food waste (kg) Woodshavings (kg) C:N ratio (%, w/w) 100.0 21.5 20:1 68.9 100.0 26.2 22:167.0 100.0 30.8 24:1 65.2 100.0 35.5 26:1 63.6Size Reduction of Feedstocks, Materials Movement in the Chamber andDischarge Efficiency.

The series of cutting blades with exterior spikes was very effective insize reducing all food waste material loaded into the chamber. Thisincluded very hard components, such as avocado seeds and whole pumpkin,also biodegradable plastics bags and packaging materials.

Size reduction and mixing of incoming food waste and wood shavings wasachieved rapidly within a 15 second period. The size reduction andmixing system was also very effective in thoroughly incorporating thefood waste into the wood shavings. This is particularly important, asthe wood shavings are required to absorb excess moisture released by thefood waste during size reduction and decomposition. The composting wastemass material produced after loading and approximately seconds mixingwas a very friable, moist, but not-wet mix ideal for in-vesselcomposting. The composting waste material mass was also observed to besufficiently porous to permit adequate air flow during processing. Goodair flow through the waste was essential to maintain high oxygen (>15%v/v) conditions for aerobic composting (Australian Standard AS 4454,1999).

The BioCorp™ biodegradable plastic bin liners were very effectivelyshredded, torn and incorporated into the composting waste material mass.The spikes mounted on the rotating mixing and cutting blades wereobserved to be largely responsible for shredding or tearing the bags.Notably, no physical evidence of the biodegradable bags was observed,even after a very short retention time of one week.

Two column-mounted blades (mounted in the middle of the chamber) werealso found to be very effective in mixing and promoting even andconsistent flow of composting material through the chamber.

The composted product was found to be easily extracted from theapparatus, being achieved through the sweeping action of a sickle blademounted close to the bottom of the composting chamber. Compost was sweptout of the chamber relatively evenly and into a discharge trolley.Approximately three rotations of the central shaft was required,occurring in approximately five seconds, to extract a 50 L vessel ofcomposted waste product. Although the discharge was very efficient, itis recommended that two vessels be fitted on the trolley to enablequicker extraction of compost by a single operator.

Food Waste Processed Over the Trial.

Actual quantities of food waste and wood shavings processed during theseven week trial is shown in Table 4. It should be noted that weeklyquantities of food waste were loaded at a maximum frequency of twice perweek as it was not possible to do this on a daily basis within thecontext of the trial.

Based on the ratios of food waste to wood shavings, it was calculatedthat the chamber capacity of the apparatus was found to be suitable forprocessing approximately 1230 kg of food waste per week. By changing theloading rate per week, the effect on the length of time waste materialwas retained and processed in the apparatus could be determined (Table4).

TABLE 4 Food waste processed by the apparatus during the trial phase.Note that varying quantities of food waste were added to produce productof various retention times of 1 to 4 weeks to permit an evaluation ofthe ideal retention time to achieve a given product quality. Plannedfood Actual food Actual wood Total material Approximate retentionApproximate Week waste loading waste shavings loaded loaded time ofloading in retention ending (kg) loaded (kg) (kg) (kg) unit (days) time(weeks) 1 1000 979 259 1.238 8.8 1.3 2 700 751 158 909 11.5 1.6 3 500482 103 585 17.9 2.6 4 300 303 61 364 28.5 4.0 5 300 300 61 361 28.1 4.06 300 300 61 361 28.1 4.0 7 300 300 61 361 28.1 4.0

Weekly batches of the composted product were readily identifiedfollowing discharge by the presence of plastic markers of differenttypes. Materials were relatively evenly discharged, though the markerswere difficult to identify upon discharge from the chamber.

Temperature and Oxygen Profiles in the Unit.

Results indicated that the temperature feedback mechanism was effectivein maintaining a relatively constant thermophilic temperature and highlyaerobic conditions (high oxygen, >15% v/v) within the compostingchamber. The pre-set temperature of 50° C. was chosen to ensure rapidbreakdown of the food waste, though at this temperature, the length oftime required for pasteurization (i.e., microbial pathogen and weed seeddestruction) was extended compared to higher temperatures around 55° C.(Miller, 1993, supra). Changes in temperature (at probe) andinterstitial oxygen concentration (average of three samples taken incross section in centre of composting chamber) over the 7 weekcomposting trial are shown in FIG. 3.

During the first three days of processing, temperatures throughout theapparatus rapidly rose to the set-point due to increasing microbialactivity, due to abundant carbon, nitrogen and oxygen present. A rapidrise in temperature is characteristic of well managed composting systems(Miller, 1993, supra). The insulation installed in the side walls of thecomposting chamber was effective in preventing excessive heat loss. Thetemperature profiles in the top, middle and bottom of the apparatus areshown in FIG. 4.

In general, the zone immediately in the vicinity of the centralrotatable shaft was on most occasions approximately 3° C. cooler thanthe edge of the composting chamber (FIG. 4 a), because 50% of the airinjected into the composting chamber occurred via the bearing housing atthe base of the chamber.

Distribution of oxygen in the apparatus was excellent. Due to the higherair flow rates around the central rotatable shaft, good oxygenation ofthis zone occurred, with oxygen contents mostly above 20% during thetrial. Oxygenation of the outer zone of the composting vessel was alsoconsidered good, with oxygen concentrations ranging from 20% near thebottom (FIG. 4 c) to 17% near the top surface of the composting wastematerial mass (FIG. 4 a). Better oxygenation of the outer zone of thecomposting chamber was expected near the base, due to closer proximityto the air injectors installed near the bottom of side wall(s). Evidencesuggests that highly aerobic conditions were maintained in thecomposting chamber, thus preventing the possibility of mal formation,which can occur when the oxygen concentration drops to below 15%(Australian Standard AS 4454, 1999). The absence of mal duringprocessing was noted in observations of untreated process air dischargeddirect to atmosphere.

Maintenance of uniform thermophilic temperatures (>45° C.) was achievedthroughout most of the apparatus, except in approximately the bottom20%. This is because this zone is in direct contact with the airinjectors installed in the side wall and in the bearing housing at thebase. Thus, materials in the upper 80% of the composting chamber shouldbe pasteurized before movement into the bottom 20% of the chamber, whereslightly cooler temperatures are maintained due to immediate contactwith injection air. This is to ensure a sanitized composted product isdischarged from the base of the apparatus.

To achieve higher temperatures in the composting chamber, the thermostatset-point could be raised to approximately 55° C., which would result inan overall increase in approximately 5° C. in the entire compostingchamber, thus reducing the time required for pasteurization.

Retention Time, Product Quality and Maximum Processing Capacity.

A number of samples of the composted product were discharged over thecourse of the trial to determine quality and level of decomposition, andcorresponding retention times. The cost/benefit equation is affected byhow much food waste is recycled per unit time, and thereforedetermination of maximum processing capacity to generate a product ofminimal acceptable quality had to be determined.

Product discharged after a one week retention time contained no visiblefood material and had started to turn brown in color, indicating thatthe product had been rapidly decomposing. The product discharged wasmoist, though no free water was released during the squeeze test(Australian Standard AS4454, 1999). A fruit/vegetable odor could bedetected from product. The product was also very fine and well textured,having appropriate particle size characteristics to be used as a mulch.

Product discharged after 2 and 3 weeks visually appeared to be morehumified and decomposed compared to product processed for one week andhad less fruit/vegetable odor. Product after four weeks visuallyappeared to be quite humified, and some earthy odor could be detectedfrom the product, indicating the composting process was nearingcompletion.

Product testing after one week indicated that the product met most ofthe requirements of a pasteurized mulch according to the AustralianStandard AS 4454 (1999). Additional curing in a pile or in perforatedcontainers may be desirable for the composted product to a higher levelof stability and pass the requirements as a fully composted mulchproduct.

Air Quality.

Treatment of the discharge air by an activated carbon gas cleanerreduced the detectable levels of volatile organic carbon compounds inthe air, which contribute to odor formation. Whilst the air dischargedby the gas cleaning unit was not odorless, the slight odors present weresimilar to cooked food, which were found to dissipate rapidly in thesurrounding atmosphere to undetectable levels. At no time wereodors—offensive, which typically occurs under anaerobic conditions(e.g., hydrogen sulfide and volatile fatty acids).

Also, at no time was malodorous air discharged by the gas cleaning unitinto the surrounding atmosphere, and as a result, no pests or insectswere seen to be attracted to the apparatus.

Condensate collected below the activated carbon filtration chamber,however, needed to be tapped off and either collected in a plasticvessel or discharged direct to sewer. Alternatively, this condensatecould be recycled in the apparatus by adding it with an appropriateamount of wood shavings so as to avoid leachate formation.

CONCLUSION

The performance evaluation of the apparatus revealed that the technologycould process efficiently up to 1200 kg of food waste per week based ona retention time of one week. Size reduction, mixing and aerationsystems performed efficiently to allow the controlled decomposition offood waste with wood shavings into a composted waste material product.Product discharged after a one week retention time was partly mature andpassed most of the requirements of a pasteurized mulch as defined in AS4454 (1999).

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

The invention claimed is:
 1. An apparatus for aerobically composting waste material in an aerated composting process, the apparatus comprising: an enclosed vessel comprising a first end wall, a second, opposing end wall and side wall(s) defining an interior vessel space; a rotatable shaft located within said vessel space; a drive means operatively connected to said rotatable shaft for driving said shaft: size reduction means for reducing the size of waste material introduced to the vessel; wherein said size reduction means divides the interior vessel space into first and second regions and defines a zone of size reduction through which waste material must pass as it passes through the vessel; said size reduction means comprising one or more cantilevered bars, blades or cutting plates rigidly mounted on said rotatable shaft and rotatable with said shaft, and one or more fixed bars, blades or cutting plates mounted on and extending from said side wall(s), wherein said rotatable and fixed bars, blades or cutting plates overlap and co-operate together to create a shearing action so as to reduce the size of the waste material as said waste material passes through said size reduction means; a loading port through which waste material may be introduced to said first region of the vessel; a discharge port through which waste material may be removed from the second region of the vessel; and a source of oxygen for maintaining conditions within said vessel suitable for the aerobic composting of said waste material; wherein, when the apparatus is in use, waste material introduced to said vessel moves from said first region through the size reduction means to said second region.
 2. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said vessel is constructed of, or lined with, stainless steel or alternative corrosion-resistant material.
 3. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said side wall(s) and/or said end walls are insulated so as to retain heat generated by aerobic composting of introduced waste material.
 4. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said internal vessel space is of an internal volume of less than 8 m³.
 5. An apparatus for aerobically composting waste material as claimed in claim 4 wherein said internal volume of said internal vessel space is within the range of 1.5 m³ to 5.0 m³.
 6. An apparatus for aerobically composting waste material as claimed in claim 5 wherein said internal volume of said internal vessel space is within the range of 2.0 m³ to 3.0 m³.
 7. An apparatus for aerobically composting waste material as claimed in claim 1, wherein at least one of the rotatable bars, blades or cutting plates rotates for a portion of its rotation directly past and adjacent to said fixed bars, blades or cutting plates.
 8. An apparatus for aerobically composting waste material as claimed in claim 7, wherein at least one of the rotatable bars, blades or cutting plates rotates for a portion of its rotation within a parallel space between two of said fixed bars, blades or cutting plates.
 9. An apparatus for aerobically composting waste material as claimed in claim 7 wherein one or more of said fixed and moving bars, blades or cutting plates include a plurality of teeth.
 10. An apparatus for aerobically composting waste material as claimed in claim 8 wherein said parallel space between said two of said fixed bars, blades or cutting plates is less than 200 mm in width.
 11. An apparatus for aerobically composting waste material as claimed in claim 10 wherein said parallel space between said two of said fixed bars, blades or cutting plates is less than 100 mm in width.
 12. An apparatus for aerobically composting waste material as claimed in claim 8 wherein said rotatable and fixed bars, blades or cutting plates are of substantially similar widths.
 13. An apparatus for aerobically composting waste material as claimed in claim 8 wherein said width of the rotatable and fixed bars or blades is within the range of 30 to 200 mm.
 14. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said loading port is located in the side wall(s) adjacent to the upper end wall.
 15. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said loading port is located in the upper end wall.
 16. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said discharge port is located in the side wall(s) adjacent to the lower end wall.
 17. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said discharge port is located in the lower end wall.
 18. An apparatus for aerobically composting waste material as claimed in claim 1 wherein one end of said rotatable shaft is mounted on or near one end wall, and the opposing end of said rotatable shaft is mounted on or near the opposing end wall.
 19. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said rotatable shaft is located centrally within the vessel.
 20. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said rotatable shaft rotates at a speed of less than 60 rpm.
 21. An apparatus for aerobically composting waste material as claimed in claim 20 wherein said rotatable shaft rotates at a speed in the range of 10 to 30 rpm.
 22. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said drive means comprises a single motor.
 23. An apparatus for aerobically composting waste material as claimed in claim 1 wherein one or more agitation bar(s) are mounted on said rotatable shaft for promoting even and consistent flow of materials through the vessel.
 24. An apparatus for aerobically composting waste material as claimed in claim 1 wherein one or more distribution bars are mounted on said rotatable shaft in the region of the loading port for assisting in loading materials into the vessel and feeding said waste material into said zone of size reduction.
 25. An apparatus for aerobically composting waste material as claimed in claim 1 wherein one or more sweeper bars or discharge plates are mounted on said rotatable shaft to promote composted material towards and out of the discharge port.
 26. An apparatus for aerobically composting waste material as claimed in claim 1 wherein free ends of said one or more rotatable bars, blades or cutting plates are shaped so as to draw material away from said side wall(s) of the vessel.
 27. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said rotatable shaft is capable of rotation both in a clockwise and anti-clockwise direction, and one or more rotating bars, blades or cutting plates, agitation bars or discharge sweeper bar/plate(s) are shaped symmetrically or otherwise asymmetrically shaped so as to draw material away from said side wall(s) of the vessel whilst rotating in either direction to allow for effective action in both directions.
 28. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said discharge port can be closed with a hatch or cover to form a watertight and airtight seal.
 29. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said loading port can be closed with a hatch or cover to form a watertight and airtight seal.
 30. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said source of oxygen is controlled so as to provide sufficient oxygen to maintain the temperature and oxygen conditions within the vessel space for composting by aerobic mesophilic and thermophilic microorganisms.
 31. An apparatus for aerobically composting waste material as claimed in claim 1 further comprising one or more temperature sensor(s) within the vessel for monitoring temperature and controlling the supply of oxygen to the vessel space.
 32. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said source of oxygen is in the form of compressed air.
 33. An apparatus for aerobically composting waste material as claimed in claim 32 wherein if the temperature, as measured by temperature sensor, drops to below a first set temperature, said source of oxygen is activated in a manner that supports increased biological activity and consequently causes an increase in temperature; and if the temperature, as measured by temperature sensor, increases to above a second set temperature said source of oxygen is activated to blow off excess heat, thereby maintaining temperatures within the desired range.
 34. An apparatus for aerobically composting waste material as claimed in claim 33 wherein said temperature sensor is located in the lower region of the vessel in a position within 250-450 mm of the lower end wall.
 35. An apparatus for aerobically composting waste material as claimed in claim 1 wherein supplied oxygen enters the vessel by one or more inlets located in the side wall(s) relatively adjacent to the join with the lower end wall.
 36. An apparatus for aerobically composting waste material as claimed in claim 1 wherein supplied oxygen enters the vessel by one or more inlets located in the lower end wall and/or located centrally in a basal bearing of the said rotatable shaft.
 37. An apparatus for aerobically composting waste material as claimed in claim 1 wherein the apparatus is provided with at least one process air outlet located in or adjacent to the top of the vessel, to discharge gas or process air from within the vessel.
 38. An apparatus for aerobically composting waste material as claimed in claim 1 wherein discharge gas or process air from within the vessel is fed to a biofiltration or odour treatment unit to treat said air prior to release to atmosphere.
 39. An apparatus for aerobically composting waste material as claimed in claim 1 wherein said fixed bars, blades or cutting plates have first and second ends and are mounted to said side wall(s) at both said first and second ends so as to extend across said interior vessel space.
 40. The apparatus of claim 1, wherein the rotatable shaft is mounted to the first end wall and to the second end wall. 